Quantifying and Mitigating Carbon Emissions in Long-Span Steel Bridge Construction: Lessons from the Anhsin Bridge in the Ankeng MRT System

Construction materials play a decisive role in the embodied carbon of large-scale in-frastructure, particularly in steel-intensive long-span bridges. This study investigates the construction-stage carbon footprint of the Anhsin Bridge, an asymmetric ca-ble-stayed steel truss bridge in the Ankeng Light Rail Metro system, with emphasis on material-related emissions. The assessment was conducted using the emission factor method in accordance with ISO 14067 and Taiwan Environmental Protection Admin-istration guidelines, covering material production, transportation, and on-site con-struction activities. Total construction-stage emissions were estimated at 55,349 tCO₂e, with structural steel as the dominant contributor (51.8%), followed by reinforcing steel (15.2%) and concrete-related materials. Although steel is associated with relatively high embodied carbon during production, it provides significant advantages for long-span bridges, including high strength-to-weight ratio, suitability for prefabrication, rapid erection, structural efficiency, and high recyclability. Three practical mitigation strategies—supplementary cementitious material substitution, optimized steel erection methods, and enhanced reuse of formwork and temporary works—were evaluated, achieving a combined emission reduction of 7.3% (approximately 4,048 tCO₂e). Benchmarking indicates that the emission intensity of the Anhsin Bridge (307 tCO₂e per meter of span) is consistent with international practice. The findings demonstrate that material-oriented optimization can effectively reduce embodied carbon while maintaining structural performance and constructability.